Some mails arrive "closed"

[LauraPresta]

For 2 years now, this is the only bug i was'nt able to solve.

 

Sometimes, mails from customers received on the shop are coming "closed" instead of "opened"

 

Ive found only one person with this bug but we never succeded to solve it.

 

Please if someone had a clue it would be very welcomed because now this is a real problem for me.

 

I tried to change hosting provider but same problem, i upgraded prestashop but still same problem... (so i get back to 1.6.0.6)

 

Thank you in advance guys.